1. Field of the Invention
This invention relates to a plasma discharge generating apparatus which provides a coil-induced plasma and is used for producing a thin film or for etching.
2. Description of the Related Art
Many devices incorporate a thin film made of metal, semi-metal, semiconductor, compounds such as oxide, nitride, carbide or boride or organic compounds such as hydrocarbon, fluorocarbon or siloxane. Such devices can be used for LSIs, magnetic recording devices, optical recording devices, semiconductor lasers, photo-conductive devices, flat panel displays, image sensors, solar cells, and so on.
Methods employing a vapor phase reaction are suitable for producing the thin films of such devices. Such methods include a PVD (physical vapor deposition) method, for example, sputtering method or ion plating method, a CVD (chemical vapor deposition) method, a CDE (chemical dry etching) method and an RIE (reactive ion etching) method. The vapor phase reaction is preferred over a liquid phase reaction for producing fine patterns.
In the vapor phase reaction, a gas is introduced in a chamber and the gas is activated. Then, the activated gaseous material is exposed to a surface of a substrate for etching or deposition.
Conventional activating methods include a thermal-decomposition method such as thermal-CVD, and a photode-composition method such as photo-CVD. Further, conventional activating methods include a plasma discharging method. In an inductive coupled-type plasma discharge producing apparatus, a loop coil, i.e., an antenna, is provided. A high frequency current, i.e., R.F. power, is supplied to the antenna causing a fluctuating magnetic field and a resulting high frequency circular electric field to be produced in the chamber by electromagnetic coupling. The high frequency electric field causes plasma discharge.
The electric field caused by electromagnetic coupling is composed of only an azimuthal component in an ideal case. However, in actual, conventional apparatus, there is a radial component of the electric field. It is believed that since the antenna has a terminal, the antenna is not a perfect circle, resulting in the unwanted radial component.
A radial electric field causes charged particles to be accelerated in the direction of the antenna. As a result, the antenna itself is sputtered by the charged particles. If the antenna is placed outside of an insulating chamber, the chamber will be sputtered. The sputtering causes contamination and affects the state of plasma discharge and/or the properties of films being deposited.
There is another problem in conventional plasma discharge producing apparatus, namely the increase of an electric potential of the plasma in the case when the antenna is placed inside the chamber. The increased potential frequently causes arcing so that the plasma discharge becomes unstable. For avoiding an increase of the potential of the plasma, the antenna is sealed by an insulator. However, the radial electric field causes the insulator to be sputtered. Therefore, the problem of contamination remains.
In U.S. Pat. No. 4,918,031, a plasma generating apparatus is disclosed which comprises a split metallic shield disposed internally of a coil to shield a plasma region from radial electric fields. However, in U.S. Pat. No. 5,234,529, it is reported that a shield as described in U.S. Pat. No. 4,918,031 while effective to avoid contamination caused by a capacitive coupling between the coil and plasma, can reduce plasma coupling efficiency. The improved apparatus disclosed in U.S. Pat. No. 5,234,529 comprises a longitudinally split, metallic shield disposed within a helical coil and disposed around an internal plasma region. The shield allows a significant capacitive coupling between the coil and the plasma region by the use of multiple slits through the shield.
However, the problem of contamination still remains even with such improved split shields.